High speed dental handpieces are commonly provided with nozzles for directing air and water in spray form towards the tips of dental burs. The water/air spray performs the dual functions of cooling the work area and clearing debris from that area. Intermixing of water and air to form the aerosol spray may occur either internally or externally of the handpiece. Patent 3,952,416 shows an internal mixing system in which a portion of the drive air is diverted and mixed with water in a chamber within the neck of the handpiece, the mixture then being discharged through a passage in the head of that handpiece. Other patents disclosing remote or internal mixing are U.S. Pat. Nos. 3,256,603 and 3,175,293. External mixing is typically provided, at least in one commercial line of handpieces, by concentric water and chip air tubes which have their discharge ends disposed immediately adjacent the heads of such handpieces. Simultaneous discharge of air and water from the pressurized line causes an aerosol spray to be directed towards the dental bur driven by such a handpiece. Other patents indicating the state of the art are U.S. Pat. Nos. 2,855,672, 2,369,880, 3,061,930, 3,815,241, 1,039,728, 3,199,196, and 1,270,736 (Ger. Pat. No.).
Co-pending co-owned application Ser. No. 109,761, filed Jan. 7, 1980, discloses a high speed dental handpiece having a single nozzle chamber receiving water and air (either chip air or drive air) from lines which extend through the handle of the handpiece. The chamber and its outlet are oval in cross sectional configuration with the long axis of the oval lying in the same plane as the rotational axis of the bur and with the nozzle opening being directed towards the tip of a mounted bur of standard length. Consequently, the oval spray pattern, elongated in a direction along the bur axis but confined in directions lateral to that axis, provides effective cooling and clearing actions for burs of shorter and longer shank length, as well as for burs of standard shank length, without the undesirable discharge of excessive volumes of water. In addition, the nozzle chamber serves as a pre-convergence chamber which effectively increases the distance between the separate outlets of the water and chip air tubes and the bur, and thereby insures proper air/water intermixing even for handpieces of smaller or miniature dimensions.
The air and water tubes leading to the nozzle chamber extend through the handle of the handpiece in generally parallel side-by-side relation. The nozzle chamber is formed by removing or cutting away contiguous wall portions from such tubes at the extreme distal ends thereof. Although such tubes are cylindrical for the most part, the contiguous wall portions approaching the discharge end of the tube assembly are flattened and such tubes are secured together with such flattened wall portions in direct contact with each other. The result is that the nozzle chamber, formed by removal of such flattened contiguous wall portions at the distal end of the spray tube assembly, is generally oval in cross sectional configuration.
While such construction has in general been found highly effective, circumstances may exist which would tend to reduce the effectiveness of the interaction between water and air in the nozzle chamber and thereby reduce the completeness of aerosolization. Should the pressure of air for spray development be relatively low, as might possibly occur when such air is bled from the drive air passage at a point adjacent the proximal end of the handpiece, the aerosol spray may include undesirably large water droplets and, if the air flow should be reduced even further, the discharge of water in spray form may become erratic.
Accordingly, it is an object of this invention to modify the structure disclosed in the aforementioned co-pending application to achieve greater aerosolization at lower air pressures. It has been found that such an objective may be attained by deforming the wall of the pre-mixing or pre-convergence chamber so that water entering that chamber is deflected into the path of air entering the same chamber. Such a construction insures that the water and air streams converge sufficiently at, or immediately upstream from, the discharge orifice to produce a high degree of aerosolization even at relatively low air pressures. The deflecting surface may be easily and effectively formed in a final stage of manufacturing the spray tube assembly by bending a distal wall portion of the nozzle chamber--specifically, a portion provided by the water tube that is located diametrically opposite from the cutout portion of that tube--so that such wall portion slopes inwardly and distally to the discharge orifice. Water impinging on the sloping surface will therefore be deflected into the mainstream of air entering the nozzle chamber from the air passage, promoting more complete aerosol development than might otherwise be achieved under low air pressure conditions.
Other objects, features, and advantages of the invention will become apparent from the drawings and specification.